Well, obviously you will be a third party, and third parties are allowed to trade information.
There also USED to be a clause about being on private mailing lists, etc, while not a part of the group, but having to have your allegiance clearly marked on ever message. I say used to, because that portion is now gone from the Spying Rules.
I'd say if you were INVITED, then it's not an "infiltration". Probably best to reply to the person issuing the invitation reminding them you are not part of the group. Then if they still ask you to participate, that's entirely their fault.
"May the Grace of Ara go with you, and His Vengeance be wrought upon your enemies."